COMPUTERA Computer is an apparatus built to perform routine
calculations with speed, reliability, and ease. In addition to this
basic function, the advance of technology has enabled computers to provide
numerous services for an ever-increasing number of people. Since
their introduction in the 1940’s, computers have become an integral part
of the modern world. Besides the readily apparent systems found in
government sites, industries, offices, and homes, microcomputers are now
also unobtrusively embedded in a multitude of everyday locations such as
automobiles, aircraft, telephones, videocassette machines, and kitchen
appliances.The three basic types are digital, analog, and
hybrid computers. Digital computers function internally and perform
operations exclusively with digital, or discrete, numbers. The most
familiar and the type on which most progress has centered, they are the
focus of the following article. Analog computers use continuously
variable parts exclusively for internal representation of magnitudes and
to accomplish their built-in operations. Thecomputer uses both continuously variable techniques
in operations.Digital, analog, and hybrid computers are conceptually
similar in that they all depend on outside instructions. In practice,
they differ most noticeably in the means they provide for receiving new
programs to do new calculating jobs. Digital computers receive new
programs quite easily, either through manual instructions or by automatic
means. For analog or hybrid computers, however, reprogramming is
likely to involve partial physical apparatuses arranges so as to enact
the specific type of mathematical relationship for which solutions are
to be computed, the choice of a new relationship may require a new assembly.
To the extent that analog machines can be considered programmable, their
program is rebuilt into their structure for each job.

HISTORY OF COMPUTERSHistorically, the most important early computing
instrument is the abacus, which has been known widely for more than 2,000
years. Another computing instrument, the astrolabe, was also in use
about 2,000 years ago for navigation.Blaise Pascal is widely credited with the building
of the first “digital calculating machine” in 1642. It performed
only additions of numbers entered by means of dials and was intended to
help Pascal’s father, who was a tax collector. In 1671, Gottfried
Wilhelm von Leibniz invented a computer that was built in 1964; it could
add and, by successive adding and shifting, multiply. Leibniz invented
a special “stepped gear” mechanism for introducing the addend digits, and
this mechanism is still in use. The prototypes built by Leibniz and
Pascal were not widely used but remained curiosities until more than a
century later, when Tomas of Colmar ( Charles Xavier Thomas ) developed
(1820) the first commercially successful mechanical calculator that could
add, subtract, multiply, and divide. A succession of improved “desk-top”
mechanical calculators by various inventors followed, so that by about
1890, the available built-in operations included accumulation of partial
results, and printing of results, each requiring manual initiation.
These improvements were made primarily to suit commercial users, with little
attention given to the needs of science.

BABBAGEWhile Thomas of Colmar was developing the desk-top
calculator a series of very remarkable developments in computers was initiated
in Cambridge, England, by Charles Babbage. Babbage realized (1812)
that many long computations, especially those needed to prepare mathematical
tables, consisted of routine operations that were regularly repeated; from
this he surmised that it ought to be possible to do these operations automatically.
He began to design an automatic mechanical calculating machine, which he
called a “difference engine”, and by 1822 he has built a small working
model for demonstration. With financial help from the British government,
Babbage started construction of a full-scale difference engine in 1823.
It was intended to be steam-powered; fully automatic, even to the printing
of the resulting tables; and commanded by a fixed instruction program.

The difference engine, although of limited
flexibility and applicability, was conceptually a great advance.
Babbbage continued work on it for 10 years, but in 1833 he lost interest
because he had a “better idea”—the construction of what today would be
described as a general-purpose, fully program-controlled, automatic mechanical
digital computer. Babbage called his machine an “analytical engine”;
the characteristics aimed at by this design show true prescience, although
this could not be fully appreciated until more than a century later.
The plans for the analytical engine specified a parallel decimal computer
operating on numbers (words) of 50 decimal digits and provided with a storage
capacity (memory) of 1,000 such numbers. Built-in operations were
to include everything that a modern general-purpose computer would need,
even the all important “conditional control transfer” capability, which
would allow instructions to be executed in any order, not just in numerical
sequence. The analytical engine was to use Punched Cards (similar
to those used in Jacquard loom), which were to be read into the machine
from any of several reading stations. It was designed to operate
automatically, by steam power, with only one attendant.

Babbage’s computers were never completed.
Various reasons are advanced for his failure, most frequently, the lack
of precision machining techniques at the time.Another conjecture is that Babbage was working
on the solution of a problem that few people in 1840 urgently needed to
solve.

After Babbage, there was a temporary loss
of interest in automatic digital computers. Between 1850-1900 great
advances were made in mathematical physics, and it came to be understood
that most observable dynamic phenomena can be characterized by differential
equations, so that ready means for their solution and for the solution
of other problems of calculus would be helpful. Moreover, from a
practical standpoint, the availability of steam power caused manufacturing,
transportation, and commerce to thrive and led to a period of great engineering
achievement. The designing of railroads and the construction of steamships,
textile mills, and bridges required differential calculus to determine
such quantities as centers of gravity, centers of buoyancy, moments of
inertia, and stress distributions; even the evaluation of the power output
of a steam engine required practical mathematical integration. A
strong need thus developed for a machine that could rapidly perform many
repetitive calculations.

USE OF PUNCHED CARDS BY HOLLERITHA step toward automated computation was the introduction
of punched cards, which were first successfully used in connection with
the computing in 1890 by Herman Hollerith and James Powers, working for
the U.S. Census Bureau. They developed devices that could automatically
read the information that been punched into cards, without human intermediation.
Reading errors wereconsequently greatly reduced, work flow was increased
and, more important, stacks of punched cards could be used as an accessible
memory store of almost unlimited capacity; furthermore, different problems
could be stored on different batches of cards and worked on as needed.

These advantages were noted by commercial interests
and soon led to the development of improved punched-card business-machine
systems by International Business Machines (IBM), and other companies.
These systems used electromechanical devices, in which electrical power
provided mechanical motion—such as for turning the wheels of an adding
machine. Such systems soon included features to feed in automatically
a specified number of cards form a “read-in” station; perform operation
such as addition, multiplication, and sorting; and feed out cards punched
with results. The machines were slow, typically processing from 50-250
cards per minute, with each card holding up to 80 decimal numbers.
At the time, however, punched cards were an enormous step forward.